Servo mechanism



All@ 17, 1937- 4 R. vc. RUSSELL 2,090,335

sERvo MEGHANISM Fild March 26, 1934 3 Sheets-Sheet 1 l' se INVENTOR. Oeff' C'. Fussell Ma-7% www ATTORNEY.

Aug. 17, 1937. 5R. c. RUSSELL 2,090,335

SERVO MECHANISM Fi'ledMafch 26, 1934 y 3 Sheets-Sheet 2 INVENTOR. oeri' C. aell,

A TTORNEY.

R. c. RUSSELL 2,090,335

SERVO MECHANISM Filed March 26, 1934 Aug. 17, 1937.

3 Sheets-,Shet 3 ATTORNEYS.

Patented Aug. 17, 1937` UNITE-D STATES PATENT oFFlcE l l SERVO MECHANISM Robert C. Russell, Detroit, Mich.

Applicationl March 26,

f27 Claims.

'I'hls invention relates to that class of power amplifying mechanism commonly termed servo mechanism and is of a type particularly applicable for operating the brakes of motor vehicles, the principal object being the provision of a device of this type ythatis simple in construction and eiiicient in operation and such as to permit the loperator to have complete control at all times over the amount of force being applied bythe l mechanism.

Objects of the invention include the provision of a servo mechanism applicable for use in con- -nection with a motor vehicle for applying the brakes thereof and obtaining its source of energy i from the rolling momentum of the vehicle; the provision of a servo mechanism for applying thel brakes of a motor vehicle through the rolling momentum thereof and so associated with -the propeller shaft of the vehicle as to receive its source of power therefrom; the provision of a mechanism of the type described so constructed and arranged that the high output forces from the servo mechanism are Vnot carried through anti-friction bearings rotating at propeller shaft gf, speed; the provision of -a mechanism of the typev described so constructed and arranged that substantially all of the relatively rotatable members are separated by anti-friction means with the exception of the elements of thefriction device thereof. Y

Other objects include the provision of a servo mechanism applicable for use in applying the brakes of a Amotor vehicle in which one of the friction elements thereof is so constructed and arranged with respect to its driving shaft that upon operation of the servo mechanism a portion of the force provided theby produces a .counter force tendlng'to resist further application of the servo mechanism by the operator, and in which the opposing force is proportional to the amount of force exerted by the servo mechanism, thereby enabling the operator to feel the amount of force being exerted by the servo mechanism; the provision of a servo mechanism that is operable regardless of the direction of rotation of its driving shaft; and the provision of a servo mechanism operable with a. minimumamount e of angular movement of its driving shaft. 4

Other objects are to provide a servo mechanism lll while increasing or decreasing such braking force.'l

.55 tothe end that satisfactory two way modulation particularly' applicable for the operation of the 1934, serial No. 717,393

(ci. iss-14o) of the braking effect on the vehicle is obtainable.

Another object is to provide a servo mechanism capable of being actuated with a minimum amount of movement of the manually controlled members therefor, the operator resorting mainly to the accurate degree of antagonistic force or reaction feel as the agent by which he gauges the force output of the servo mechanism, the minimum movement required for complete actuation of the mechanism reducing the physical effort required for its operation.

A further object is to provide a servo mechanism of the type described that is low in weight, small and compact in design and composed of parts which lend themselves readily to low cost production and are not subjected to undue stresses in operation.

'I'he above beingamong the objects of the present inventiomthe same consists in certain novel features of construction and combinations of parts to be hereinafter described with reference to the accompanying drawings and then claimed, having the above and `other objects in.

view.

In the .accompanying drawings which illustrate suitable embodiments of the present invention and in which like numerals refer to like parts throughoutthe several dlierent views,

Figure 1 is a more orless diagrammatic, par. tially broken, side elevational view of a motor vehicle illustrating the application of a servo mechanism thereto for the purpose of actuating its brakes. Y

Fig. 2 is an enlarged vertical sectional view taken centrally through the servo mechanism shown applied to the motor vehicle in Fig. 1, the mechanism being shown in inoperative position.

Fig. 3 is a slightly reduced view of va portion of the mechanism shown in Fig. 2 but with certain of the parts not shown in section so as to better illustrate the same, \and also indicating the servo mechanism in an operativev position.

, Fig. r4 is a transverse sectional view taken on the line 4-4 of Fig. 3.

Fig. 5 is a side elevational view,v partially in section,v illustrating a modified form of cam means for theservo mechanism illustrated in the preceding views. Fig. 6 is a vertical sectional view taken transon theline 6-0 of that figure.

versely of the vmechanism illustrated in Fig. 5 as side elevational view of a modified form of drivs ingconnecti'on between themanually operable vfriction element and the power shaft.

I 10 side elevational view of the-servo mechanism illustrated in previousviews and illustrating a construction preferably provideddor limiting application oi the servo mechanism when the linings -of the brakes operated thereby are worn -to va.A

l point where they need adjustment.

Fig. 11 is a v ie'w similar to Fig. 10 but illustrating a modification of the construction shown in Fig. when the operated shaft of the servo mechanism is] placed below center instead =of :i0 above center as illustrated in the previous views.

. Fig. l2 is a view similar to Fig. 10 but illustrating the application of the servo mechanism tol brake mechanisms of the hydraulic type.

` Fig. 13 is a fragmentary plan view of the mech- 15 anism shown in llg. 1 2.

It is well recognizedin the motor vehicle art that the modern tendency is toward greater ease of operation of the various controlling elements thereof so that the operator will need to expend only a minimum amount of physical eilort 'in easily and surely controlling the operation of the vehicle. Toward this end various constructions have been provided or suggested for power operation of the vehicle brakesfor it is the brakes that usually require the greatest amount of physical exertion on the part of the vehicle operator during operation of the vehicle. In the past there have been several auch classes of brake mechanisms developed, some of which employ 40 artiilcially created air pressure, some of which employ the suction existing in the intake manifold of .the engine provided for driving the vehicle as the source of power. some of which have empl9yed the pressure of the lubricant in the engine lubricating system as a source iol power, and still others which have employed the -momentum of thevehicleasasourceofpower. Itistothis last class of devices. vwhich are commonly known ss "servo" mechantsms,'that the present invention is directed, although it will'be understood solely to its application to motor vehicles for the purpose of applying the brakes thereof, its" application to other uses will be readily apparent `otothoseskilledin'theart; 'v-

There-have been various disadvantages in eonstructions heretofore Proposed for mechanical servo mechanisms of the type described; lOne of the'chief diillculties has beenfthat in prior con- 4mi strwc'tions it has been impossible or substantially impossible for the operator of a vehicle, in operating the servo mechanismto apply the brakes, to feel the amountof force exerted by the sem mechanism during such application-and conse'- quently he has no "yard stick" 'bywhichbe may applied to the vehicle. disadvantage has been in prior constructions of mechanical"servo type that it has been substantially vs impossible to accurately control the CWM of braking eilort elected by the servo mechanism and particularly to gradually reduce the braking eil'ort from a position of maximum effort in amounts and in degrees proportional to the relief of pressure on the control element by the opera- 5 tor of the vehicle. l'A further disadvantage has o been that in the operation of such prior servo mechanical mechanisms it has been necessary for the operator o! the vehicle to move his foot through substantially the same range of movei0 ment as is customary in purely manually operated brakes whereas, to obtain a maximum degree of ease and comfort in the operation of the brakes. theoperator should be required to move his foot only a minimum distance. 'Ihese and other disl5 advantages of mechanical servo constructions heretofore suggested are overcome by the structure provided in 'accordance with the present invention.

Referring now to the drawings, in Fig. l there 20 l is indicated in a more or less diagrammatic manner a motor vehicle having a pair of front wheels 20 and a pair ofrear wheels 22, each of which is provided with a brake mechanism indicated generally at 2l and each of which brake mechanisms 25 is provided with an operating arm or lever Il.. 'I'he vehicle is also shown as including an engine 28 at the rear end of which is located a suitable type of clutch mechanism contained within the clutch housing Il secured to the rear face of 30 the engine .2l in a conventional manner. A transmission casing 32, which may contain any suitable or conventional transmission or change speed gearing, is secured to the rearvend of the clutch housing 3l in a conventional manner,` 35 and a casing M which serves as a housing tor It completes the power transmission line between 4o the engine 2l andthe usual rear axle (not shown) connecting the rearwheels Il in the usual manner.

vReferring now to Figs. 2 to 4, inclusive, and f particularlytolligzitwillbenotedthatthe 46 servo casing $4 includes a removable rear portionorcoverllwhichmaybesecuredtothe main portion thereof by screws Il or other suitable means. Alsoreferringto Fig. 2' it will be f noted that the rear end ofthen transmhl:se sion shaft Il is provided with a suitable .bear. ingassembly Il inthe rear wall of the transand-theredueed forward end of the servo shaft -isreceived therein and provided with suitable bearings 4l permitting relative rotation between itandthe main transmission shaft Il. rear end of theservo shaft is suitably supso ported in a'bearing assembly Il which in turn The is supported internally `of a forwardly projecting sleeve I! formed integrally with the cover Il eoneentrleally with the shaft Il. Thebearingseeembly llismaintainedagslnst 05 axial displacement relative tothe sleeve Il by its outer race ,abuttingv a1 radial shoulder Il formed internally thereof at one end and a contractible split springstop ring It sprung into a o cooperating annular groove formed internally of `7o properly Judge the degree of brakingeii'ort being `the sleeve I2 at the opposite end. A'111e shaft 'is maintained against axial displacement through the bearing assembly Il the of which sbutsatoneendagainstasplitspringstopring the shaft 46 and against which it is maintained by the hub of the flange member' 68 of a conventional type universal joint 62 (see Fig. 1)

and which flange member is splined to the shaft 46 and secured against axial displacement thereon by means of a nut 64. o

In the particular illustration given, the shafts 42 and 46are shown as being drivably connectedv together through the intermediary of an overrunning clutch or free wheeling unit indicated generally as at 66 and which may be of any suitable or conventional design and which may include, for instance, a shiftable clutch element l68 for locking ,the free Wheeling unit 66 against gears provided for operating the usual speedometer and likewise form no part of the present invention.

Rotatably and axially slidably mounted upon the shaft 46 immediately to the rear of the gear 18 is a friction brake member indicated generally at 13 .and including a hub portion 14 embracingthe shaft 46, and an outwardly and rearwardly extending web portion 16 supporting at its periphery a frusto-conically shaped rearwardly extending portion 18. The following means are provided for causing this brake member to rotate with the shaft 46. "A ring member 88 surrounding the shaft 46 rearwardly or to the right ofthe hub 14 is secured for equal rotation with the shaft 46 by means of a pin 82. 'I'he forward axial face of the ring member 88 40 is provided with a pair of diametrically opposed forwardly opening notches 84 therein. Another ring member 83 rotatably surrounds the shaft 46 forwardly or in advance of the ring 88 and is provided with a pair of rearwardly extending 45 teeth or lugs 88 on its rear face which are axially and radially slidably received inthe notches 84, the latter movement being possible to a small extent because the ring 86 has a relatively loose fit on the shaft 46. The forward axial 'so face of` the ring 86 is provided with a pair of.

diametrically opposed forwardly and axially tapered teeth 88, each of which is received in a correspondingly shaped rearwardly facing notch 82 formed in the rear edge of a ring member 84 secured by rivets 86 to the web 16 of the previously described brake element. The teeth 88 are disposedmidway between the teeth 88 about the axis of the shaft 46, and it will be apparent that this arrangement of the teeth 88 and 88 and their engagement with the notches .84 and 82 respectively provides a connection of a type similar to that found in an Oldham coupling y and, as will hereinafter be understood to be desirable, permits an equalization of the pressure 55 between the teeth 88 and the side walls of the corresponding notches 82 so as to compensate for any manufacturing tolerances which might otherwise prevent it. For the purpose of effecting this type of drive, it will be understood that the center ring 86 surrounds the shaft 46 in a more or less loose condition in comparison to the fit of the other elements. It will also be understood, and as indicated in Fig. 2, when the servo mechanism is in inoperative position, a certain amount of axial play is provided between free wheeling operation. The free wheeling unit the rings 88, 86, and 84. It may be noted in passing, and as will hereinafter be apparent, that whether the teeth 88 and notches 82 are reversed in position on the rings 86 and 84 or not makes no difference inthe functioning of the device.

A thrust Abearing indicated generally at 98 is fitted about the hub 14 of the friction element 13 with its rear ring in abutting relationship to the forward face of the web 16, and the free ends of a. yoke member |88 straddle the hub y14 and bear against the forward face of the forward ring of the thrust bearing 88 at diametrically opposite points thereon. ,The yoke member |88 is pivotally mounted within the casing 34-by means of opposite end shaft sections |82 one of which is suitably connected to a manually operable lever convenient to the operator of the vehicle in a manner which will be described in detail later. However, it` may be noted at this point that rocking of the yoke |88 about the axis of the shaft |82 in a counter-clockwise direction will act to force the brake element 13 in a rearwardly direction or to the right as viewed in Fig. 2.

The sleeve 62 formed on the cover 38 projects Iforwardly over the ring members 88 and 86 and to a point over the ring member 84 and at its for` ward end is externally provided with a split spring stop ring |84 received in a suitable groove provided therefor in the sleeve 52. A thrust bearing assembly including balls |86 surrounds the .sleeve 62 and its forward ring |88 abuts the stop ring |84. The rear member of this thrust bearing includes a member ||8 whose forward face is of planular formation for rolling engagement with the balls |86. The member ||8 is radially extended beyond the ring |88 and secured there- A to as by means of rivets ||2 is a second friction element, indicated generally at ||3, provided for cooperation with the element 13, and which includes a cone element ||4-the outer face of which is provided with a suitable friction material ||6 complementary in shape and disposed within the portion 18 ofthe brake element 13.

As perhaps best indicated in Figs. 3 and 4, the rear axial face of the member ||8' is formed to provide four axially inclined cam surfaces |28 cooperating to form two diametrically oppositely disposed rearwardly projecting cams or teeth |22. Slidably surrounding the sleeve 62 immediately rearwardly or to the right of the member ||8 is an axially slidable bearing member or sleeve |24, the rear end of which is provided with a radially outwardly extending annular flange |26. Pressed upon the sleeve |24 in fixed relation therewith and in abutting relationship with respect to the ange |26 is a member |28l the forward face of which is formed to provide four axially inclined cam surfaces |38 cooperat- .ing to form a pair of forwardly extending cams or teeth |32 complementary to the cams or teeth |22 on the member l I8. A pair'of diametrically oppositely disposed rollers |34 are disposed between the members ||8 and |28 and in contact with the respective cam surfaces thereof, the rollers |34 being maintained against relative displacement with respect to each other by being rotatably mounted upon the radially disposed pins |36 fixed to and projecting inwardly from the ring member |38 disposed about the members ||8 and |28.

A horizontally disposed cross shaft |48' extending through and having suitable bearing in the co'ver 38 has spllned thereto interiorly of thek housing a yoke member |42. The free ends of the yoke member |42 bear against the stepped rear face of the member |28. Pins |48 connect the free ends of the yoke |42 with the member |28 so as to maintain the member |28 against rotation.

. As best indicated in Fig. ,10, the shaft |48 projects to the exterior of the cover 88 and there has fixed to it a depending arm |44. the lower end of which is pivotally connected by means of a pin |48 toa rod |58.- Now referring to Fig. 1, it will'be noted that the rear end of the rod |58 is connected by means vof a pin and siot connection with the end. of a lever |52 secured to a brake cross shaft |54. At each of its opposite endsthe brake cross shaft |54 is provided with an upwardly extending arm or lever |58 and a downwardly extending arm or lever |88, the upwardly extending levers |58 eachbeing connected by a rod |88 to the operatinglever 28 for I the corresponding brake 24 on the respective rear wheels 22, and thedownwardly extending arms or levers |58 each being connected by'rods |82 with the corresponding operating arm or lever 28 for the corresponding brake 24 for the front wheels 28. A rod |84 may be connected atits `rear end by a suitable pin and vslot connection with one of the levers |58 and at its forward end to 'a' suitable vemergency brake lever (not shown), this pin and slot connection permitting normal operation of the brakes in service without affecting the position of the emergency brake lever and the pin and slot connection between the rod |58 and the lever |52 permitting operation of the emergency brake lever without affecting the position of the elements of the servo mech-- anism.

As indicated in Figs. 1 'and 1o and best shown' in Fig. 10, a coil spring |18 is maintained under tension between the arm |44 and a lug |12 formed on the side, of the housing 84, this spring constantly urging the arm |44 and shaft |48 in a clockwise direction of rotation' as viewed in.

these figures. Referring now to Fig. 2, it will be noted that the shaft |48 in being urged toward a clockwise direction of rotation will act4 through the yoke |42 to urge the member |28 forwardly and this force will be transmitted throughthrollers |84 tothe member ||8, ballsv |88 and member |88 and' will'A force all 'of these members forwardly until the member |88 abuts the ring |84 against which it is constantly'maintained. As also indicated in Fig. 2, the rollers |84 are, when the servo mechanism is in inoperative position, located at the low points of the v cam surfaces I|28 and |88 or, in other words, at the base of the cams |22 and |82 which thus permits the members |18 and` |28Y to approach each other in such a manner that their combined axial length is at a minimum value.- It may also `be noted that the usual spring means (not shown) found within the brakes 24 as in all conventional wheel brake mechanism -and constantly tending to release the brakes. act through the various rods, arms and levers heretofore described which are interposed between them and the arm |44 o to supplement the action of the spring |18. The

spring l|18 is provided primarily for the purpose of maintaining the various parts of the. servo mechanism and particularly the members |"|8,

|24 andiroll'ers I|84 in their normal positions duringthose periodsfthat the wheel brakes are'apj plied, through the emergency brake lever.

In the operation of the device, `parts to be in the positions indicated in I||ig.'2,f dthatis, in inoperative "position, and vehicle in motion, it will'be understood that the shaft y The friction element ||8 will be stationary, its friction -facing ||8 slightly spaced from the cooperating face of the friction element 18, the rollers |34 at the bottom of the respectlve cams |22 and |82 s'o that themembers I8 and |28 are in a position of minimum axial displacement, and the shaft |48 and yoke |42 rotated to `their extreme position of. clockwise movement as viewed in Figs. 2 and 3. Underv such conditions let it be assumed that the operator of the'lvehicle, through suitable control means which may be of any suitable type and but one of which will hereinafter be more fully described, causes the shaft sections |82 and yoke |88 to be'v rotated in a counter-clockwise direction as viewed in Figs; 2 and 3. When this occurs the free ends of the yoke |88 will press rearwardly against the thrust bearing 88 which, in turn. will cause the friction element 18 to be shifted axially rearwardly, it being understood that provision for such movement is provided in the connection between the members 88, 88 and 84, until the frusto-conical portion 18 of the friction element 13 engages the friction element H8. Inasmuch as only a slight amount of clearance is normally provided between the members 18 and ||8, but a slight amount of bodily movement of the friction element 18 will be required to ei'fect such engagement, and accordingly a oorrespondingly small amount of movement vofthe control element operatedby the operator of the vehicle will be required.

Assuming that'the vehicle is in motion and consequently that the shaft48 is rotating when such engagement between the members 18 and ||8 occurs, the member 18 in being forced to rotate with the shaft 48 will urge the member ||8 toward equal rotation with it. The member ||3 will, in fact, rotate a limited amount with the element 18 depending upon the force of engagement between the members 18 and ||8 as will hereinafter be more apparent, and in so rotating will cause the rollers |84 to roll along "its cam faces |20 and toward the point of the camv Therollers |84, however, being frictlonally engaged between the members ||8 and |28 and the I member 28 being maintained against rotation, the rollers |84 will roll along the cam surfaces |28 and bodily move the rollers |84 about the axis of the shaft 48 at only half of the speed and for only half of the distance that the surfaces |28 move. At the same time the rollers |84 will roll up the cam surfaces |88 of the member |28 toward the point of the cams |82 thereof, thus acting to further separate the members ||8 and |28.

From the foregoing it will be observed that because of the fact the rollers`|84 will move bodily v lin the same direction of rotation as the member I8 but at only one-half the angular speed thereof and through only'one-half of the distance which any particular point on the member ||8 moves! Y..

during such rotation, and further that because.V

ln the particular illustrations'given in Figs. 2. 3,

the rollers 84 from the bottoms of the cams |22 to the tops or points thereof. Likewise, because of the fact the cam surfaces |88 and cams |82 on the member |28 are directly opposed to those on the member fl i8; the rollers |84 in being carried, along the cams 22 will also be carried .up the cams |32. From this it will be understood that in a case where the rollers 34 were permitted to move the full distance from the bottoms, 5 of the cams |22 and |32 to the tops thereof the member I would rotate through 180 degrees of movement and consequently will force the members ||0 and |28 axially apart by a distance equal to the sum of the height of the cams |22 10 and |32. 'I'hus by this construction a maximum amount of lift is obtained by-cam surfaces which are so constructed and arranged as to move relative to each other a maximum distance ln comparison to their individual length, resulting l in a maximum amount of mechanical advantage, but on the other hand, as far as a brake servo mechanism is concerned, it is capable of being fully operated with a minimum amount of rotation of the driving shaft.

Under the conditions above explained, as the rollers |34 roll up the opposed cams |22 and |32 on the members ||0 and |20 respectively, the member ||0 is maintained against forward displacement through the stop ring |04 and conse,-D 25 quently the member |28 is forced rearwardly on the sleeve 52. In moving rearwardly the member |28, because of its cooperation with the free ends of the yoke |42, will cause the yoke |42 and consequently the shaft |40 to rotate in a counter- 30 clockwise direction of movement and through a distance depending upon the amount of rearward movement of the member 28. The shaft |40 in rotating in a counter-clockwise direction will cause a similar movement of the arm |44 which, 3 acting through the rod |50 and lever |52, will cause the brake cross shaft |54 previously described 'to rotate in a counter-clockwise direction as viewed in Fig. 1 and cause -application 'of all of the brakes 24.

As the brakes 24 are applied as above described it will be apparent that resistance to rotation of the arm |44 and consequently rearward movement of the member |28 will increase. When the amount of resistance to rearward movement ofy 45 the member |28 divided by the mechanical, ad-

vantage obtained through the cams |22 and |32 and rollers |34 equalsv the friction exerted between the friction elements 13 and ||3, slippage will occur between these last two membersh and rotation of the friction element ||3' and further application of the brakes will-:be stopped. If at this point a greater braking effort is desired, greater pressure is applied by the operator tending to rotate the yoke |00, thus increasing the friction between the elements 13 and ||4, and further rotation of the element ||3 and corresponding rearward movement of the member |28 with its corresponding further application of Athe brakes 24 will occur untilthe added resistance to application of the brakes again overcomes the friction set up between the elements 13 and 3 at which time these elements will again slip relative to one another and rotation of the element ||3 and further application of the brakes cease.

The above' described slippage between the friction elements 13 and 3 during application of the brakes will, of course, generate a -certain amount of heat: and for the purpose of preventing overheating of the parts of the mechanism and to foster the rapid transfer of heat tovthe casing 34 where'it may be readily dissipated, as -well as to provide ample lubrication for the mechanlsm, the casing 34 is preferably partially lled 75 with a relatively light lubricant which will be thrown about by the rotating parts and constantly bathe all of the mechanism. V

It will be apparent that inasmuch as the degree of compression of the friction facing IIB will ordinarily be relatively slight,` once the yoke is moved to bring the elements 13 and ||3 into en-y gagement with each other only a relatively slight additional movement of the control element under the control of the vehicle operator willl be required to effect a higher degree of braking action and, accordingly, a very slight amount of movement of the elements under lthe control of the vehicle operator to effect actuation of the brakes will be required.

It will also be noted that the power actually provided for operating the brakes is derived from the shaft 46 which is drivingly connected to the road wheels of the vehicle at all times and conse.- quently, assuming that the brakes are only applied when the vehicle is moving under its own 4momentum, the amount of power available for the actuation of the brakes is directly proportional to the speed of the vehicle and consequently the braking requirements of the vehicle. In this connection it may be noted that the amount of effort required to be exerted by the vehicle operator in effecting a high degree of power transmission between the shaft 46 and the brakes is enhanced in the construction shown by the use of thev 4speed which must carry the braking force exerted by the servo mechanism and that for this reason not only may the various parts be made of relatively light construction but it also enhances the long life of the construction in general. While the thrust bearing including the balls |00.is subjected to the force output of the servo mechanism, nevertheless it will be recognized that upon each application of the vehicle brakes these balls merely operate at a maximum of 180 degrees of rotation of the member ||3 under conditions of maximum movement which seldom, if ever, will occur in the construction. It might also be noted that as a precaution to prevent possibility of the rollers |34 from rolling over the points of the cams |22 and |32 under unusual conditions of -Wear or operation, the width of the member |20 is preferably so regulated that the flange |26 of the bearing sleeve |24 will contact with the rear wall of the cover 33 before the rollers |34 reach the tips of their cooperating cams |22 and |32,

1 and consequentlyit is impossible for the rollers |34 to roll over the points of their cooperating cams.

It may also be noted that as soon as the vehicle operator releases the pressure applied to the yoke |00 tending to set the brake, the frictional engagement between the members 13 and I |3 will be relieved, at which time the` force of the spring and the usual springs contained within the brakes 24 and previously referred to will tend to move the shaft |40 and yoke |42 toward their normal position indicated in Fig. 2. The pressure thus exerted by the yoke against thevmember tending to force it forwardly, because of the rolling engagement between the rollers |34 and the members H8 and |28 'and the angularity of the cam surfaces |28 and |88, will be sumcient to cause the member i I8 and the element I I8 carried thereby to rotate back to their normal positions in which the rollers |34 are located at the low point of the cam members. Because of the fact that the member H8 is backed up by a thrust bearing including fthe balls |88. and because. of the rolling engagement provided by the rollers |84.between the members H8 and |28, only a small amount of pressureneed b e exerted by the yoke |42 against the member |28 to thus return the parts to their normal inoperative positions.,

As a matter of fact it has been found that perl haps not more than five per cent of the total force exerted by the spring |18 and the spring means within the wheel brakes 24 constantly urging the wheel brakes toward inoperative position is required to return the parts of the servo mechanismA to their normal inoperative positions upon the release of the control member by the vehicle operator. The construction has beenparticularly designed to obtain such a condition for the reason that the smaller the amount of power re- 25 quired to return the mechanism to its inoperative position the more sensitive is the control of the servo mechanism by the vehicle operator. To

' illustrate this point let it be assumed that instead of ilve per cent ofthe force of the springs |18 and the springswithin the wheel brakes 24, ninetyve per cent of the force of such springs was required to move the mechanism to inoperative,

pressure required to move the present mechanism Etoward released position, full and complete moduv lation of the braking effect on the vehicle by the servo mechanism may be obtained either while the brakes are-being moved toward applied position or from applied position. This capability of complete two way modulation is an important advantage of the present invention over structures heretofore suggested.

An important feature of the present invention 551s the reactive feel provided by the mechanism` described, in the operator so as to enable him to be conscious 'of and determine the amount vof braking force exerted by the servo mechanism at any time during the operation oi' the brakes. This feel is obtained for the following reason. As previously described, the friction element 18 is constrained for equal rotation with the shaft 48 through the ring member 84, teethv 88, ring member 8|, teeth 88 and ring member 88. However,

' 65 when the members 18 and III are brought into engagement to effect operation of the brakes and the member H8 has rotated to a position of balance between the amount of friction exerted between itself and the member 18 and the resistance offered by the application of the brakes to further rearward movement of the member |28; the friction exerted between the members 14 and H8 will tend to prevent the member 18 from rotating with the shaft 48 and this tendency toward retardation oi' rotation of the member 18 is @sodass overcome by engagement of the teeth 88 in the notches 82 of themember' 84. Because the cooperating faces of the teeth 88 and notches 82 are inclined axially, the pressure exerted therebetween in compelling the member 'I8 to rotate with the shaft 48 under such conditions has an axial component tending to separate the members 88and 84 and consequently to separate the friction elements`|l8 and 18. The force thus exerted tending to move the friction element 18 forwardly reacts against the yoke |88". tending to turn it toward brake released position, and this tendency is made apparent to the operator of the vehicle by the reactive pressure in the ccntrol pedal or element actuated by the operator to apply the brakes. 'I'he amount of reactive force thus made apparent to the vehicle operator and which is the axial compo-nent of the force tending to rotate the friction element 18 with the friction element H8 is ofcourse, directly-l proportional to I the amount of friction set up between the elements 'I8 and I I8 and consequently directly proportional to theforce output of the servo mechanism. Consequently, the vehicle coeiilcient of friction between the members I8 and III and regardless of any particular degree of movement of the control elements operated by the vehicle operator. The amount of such reactive force made apparent to the vehicle operator may,

of course, be varied byvarying the angularity of l the sides of the teeth 88 and notches 82, the

greater the angle .between the sides of the teeth 88 the greater the reactionary force apparent to the vehicle operator, and the smaller the angle between the sides gf the teeth 88 the smaller the ator.

As has been previously described, the driving engagement between the rings 88, 88, and 84 including the teeth' 88 and 88 form in effect an Oldham coupling because of which the force exerted between the two teeth 88 and the side faces of their cooperating notches 82 will be equallzed at all times, thus insuring freedom from friction or sticking tendencies, and uniform oper-l ation and wear oi' the parts.

In the foregoing descriptionof the operation of the mechanism no mention has beenmade of the direction oi' rotation of the shaft '48. This has been for the obvious reason that it makes no diii'erence in the construction illustrated in Figs. A

2 to 4, inclusivewhether the shaft 48 is rotated in one direction or another as the operation will be identical in both cases and, accordingly, the mechanism herein provided and heretofore described permits equally eiiicient operation of the brakes by the servo mechanism regardless of the direction of rotation of the shaft 48 and consequently direction of travel of the motor vehicle of which it forms a part.

It may occur desirable in some cases, however. i

or a doulable'prirxie mark. It will also be noted that the construction shown in Figs. 5 and 6-is modified over that previously described in that the i with 'the exception that they carry either a prime aoedsst 'members H0 and |28 areeach provided with three cams |22 and |32 respectively instead of two cams as in the previously described construction. This may be preferable under certain circumstances to better balance the transmission of forces between the members H and |28'. A more important feature of interest, however, 1s that while in the 'previously described construction the cam surfaces |20 on the member ||0 and the cam surfaces |30 on the member |28 are all of the same length and extend to the same angular extent about the axis of the shaft 46, in Figs. 5 and 6 the cam surface |20' on one side` Yoi' each ofthe cams |22 is longer or -extends i5 through a greater angular extent' about the axis of the member |'|0 than the opposite surface of the' cam, the longer surface |20 being so located that the rollers |34' will roll up such surfaces when the brakes are applied while the ve- 20 hicle is in forward motion and will ride up. the

shorter surfaces |20" when the brakes are applied while the vehicle is in rearward motion.

Likewise, the cam surface |30' of each cam |32' y on the member |28 is made of the same length or angular extent as the surfaces |20 on the member ||0 and the surface I 30'. the same length or angular extent as the surfaces |28" on the membqer ||0' and so arranged that the rollers |34 will roll up the longer surfaces |20 and |30' on both 30 members ||0 and |28' during application of the brakes when the vehicle is in forward motion, and up the shorter'surfacesl20" and |30" when the brakes are applied while the vehicle is in rearward motion.1 .f 3 Should it be found either desirable or necessary to further increase the sensitivity of the connection between the elements manually vcontrolled by the vehicle operator and the servo mechanism,

this may be accomplished in the manner sug 45 viously described. In this modication the con` struction of the ring 86 is identical to the construction of/ the ring 86 previously described as far as the rear, or right hand portion thereof as viewed in Fig. 7, is concerned but in this case the 50 forward portion of the member 86 is provided with a forward extension 81 projecting within the rear end of the ring 94 and which'extension 81 m carries a pair of diametrically opposed radially outwardly extending pins 89 upon each of which 55 is rotatably mounted a roller 90' received within the corresponding notch 92 of the ring member 94 and serving the same purpose as theteeth 90 previously described. The rollers 90' may be either straight, tapered as shown, or of any other 60 desired conformation so long as they provide the proper rolling contact with the sides of the notches 92.

In the construction above described it will be apparent that the servo mechanism is operative 65 to apply the vehicle brakes at any time during movement of the vehicle either in a forwardly or rearwardly direction. Even though the `Avehicle is not moving, the brakes may still be applied by the vehicle operator through the servo mecha- 70 nism upon operation of the brake control element by the vehicle operator, for uponl such operation the yoke |00 will be rotatedv to force the friction element 13 rearwardly into engagement with the friction element 3 and further 75 movement of the yoke |00 will cause both of these friction elements to move bodily rearwardly, carrying with them the members ||0 and |28 and thus act to rotate the yoke |42 and apply the brakes. While it would not be possible in this way to apply nearly as great a brakingforce as would be possible through operation of the servo mechanism, nevertheless under such conditions should actual movement of the vehicle occur the servo mechanism will immediately respond to exert its added effort. That this would occur upon a relatively slight movement of the vehicle will be evident when it is understood that the servo mechanism may be fully operated upon less than half ofthe revolution of the shaft 46 which rotates directly with the propeller shaft 36 and which propeller shaft is driven under normal conditions at from four to 'five times the speed of the rear wheels.

As previously mentioned, although any suitable or desirable form of means controlled by the operator of the vehicle may be provided for operating the above described servo mechanism through rotation of the yoke |00, it is preferable, in order to realize all of the advantages of the construction and relieve the vehicle operator of exertion in the application ofthe brakes to the fullest extent, that some means necessitating as little movement as possible of thefvehicle operators foot be provided for controlling the brakes. One such construction is illustrated in Figs. 1 and 9 and which is so constructed and arranged as to provide a cbmmon control means for both the 4brakes and the engine throttle.l As best shown in Fig. 9, this control means includes a pedal member |1| pivotally supported at |12 on a lbracket |14 which, in the particular illustration, is shown as being suitably secured to the toe board |16 of the vehicle. To the forward or upper end of the pedal |1| a plunger |18 is piv' otally connected by means of a pin |80. The plunger/|18 projects downwardly through the toe board |18 and its lower end is recessed as at |82 and slidably receives therein the enlarged head |84 of a control rod |86 operatively connected, as

illustrated in Fig. 1, tothe throttle control leverr 'plunger |18 in a downward direction, while conit will be obvious that downward pressure on the forward or upper end of the pedal |1| will depress the plunger |18 which, acting against the head |84 of the rod |86, will cause the carburetor throttle valve to be opened so as to increase the l speed of the engine 28. If the pedal |1| is operated in the opposite or clockwise direction of rotation from the position indicated in Fig. 9, as by pressure from the heel of the vehicle operator.

the plunger |18 will move upwardly and the head A |84 of the rod |86 will move downwardly in the recess |82 without causing any movement of the rod |86 and consequently the engine throttle.

A bracket member 94 is suitably secured to the under surface of the toe board |16 between the bracket |14 and the plunger |18. An arm |96 is pivotally connected between its ends by means of pin |88 to the bracket |94. The forwardend of the arm |96 is provided with a pin 200 slidably received in a slot 202 extending axially of and diametrically through the plunger |18 so as to permit a lost motion connection between the arm |66 and.the plunger |16. The opposite end of the arm 96 is connected by a pin 204 with one end'of a link' 206. As illustrated in Fig. 1the opposite end of the link 206 is pivotally connected to one arm of a bell crank 206 'pivotally .mounted at 2|0 on the clutch housing 36. The opposite arm of the bell crank 206 is pivotally connected by means "'of a rod 2|2 withan arm 2l4 secured to one of the shaft sections |02 for the yoke |60 and which shaft section projects to the exterior of the casing J4. A

Referring now to Fig. 9 in which the various parts are illustrated in their normal inoperative positions, that is, with the brakes released and 15. with the engine throttle closed, it will be noted that the pin 200 is located at the bottom of the slot 202. lAccordingly, when the pedal Ill is operated to open the engine throttle the pin 200 will slide up into the slot 202 without causing any 0 operation of the arm |66. However. if the pedal |1| is rotated from inoperative position in the opposite or clockwise direction of rotation about the pin |12 and during which movement no operation of the engine throttle valve occurs, the` forward end of the arm |66 will be lifted and thtd arm |66 will be caused to pivot in a clockwise direction of rotation as viewed in Figs. 1 and 6 about the pin |66. When thus moved the arm |66 acting through the link 206 will cause the bell crank 206 tobe rotated ina counter-clockwise direction of movement and will cause the rod 2|2 to move forwardly and rotate the arm 2| 4 and shaft section |02 in a counter-clockwise direction of rotation which will thus move the yoke |00 to 5 place the servo mechanism in brake applying position. Accordingly, with the structure provided in Fig. 9 a common means is provided for operating both the engine throttle and the servo brake mechanism and with such construction it is unnecessary vfor the vehicle operator to remove his foot from the pedal lli in order to controlboth the engine and the brakes of the vehicle.

It will be obvious to those skilled in the art that to obtain the maximum mechanical advantage of 5 the servo mechanism it would be necessary upon each application of the brakes that the rollers |34 move from a position adjacent the bottom of the cams |22 and |32 to a position adjacent the tops or points thereof and thateffective operation of the brakes begin immediately upon movement of the rollers |34 -from their inoperative positions. However, due to the fact that as the linings for the brakes 24 wear it will be necessary for the rollers |34 to travel further up the cams |22 and |62 to effect full application of the brakes, such condition is not commercially practical as it would necessitate constant re-adjustment of the brakes to take up the wear of their linings. Accordingly, it is necessary to so proportion the various elements of the structure that the'rollers |34 will move only a portion of their total possible travel in moving the brakes from their points of initial, engagement to fully applied position during a single application of the brakes. At the same time, however, this movement should be as much as possible without requiring too frequent adjustment of the brakes 24 to take up the wear of their linings, and it will be assumed that the structure shownds so constructed and arranged.

Under such conditions it is desirable to'provide some means of informing the operator of theye hicle when the brakesv have reached a condition of wear which makes it advisable to adjust them to compensate for such wear. Furthermore, such means is so constructed and arranged thatthis brakes have worn to such an extent that added application of power by the servo mechanism is. of no avail in increasing the braking effect-.j Buchconstructions are illustrated in Figs. l0ifto 1 6, in?l elusive. Referring now to Fig. l0, it will be that the arm |44 is provided adjacent its hub with a forwardly extending boss-like ann 226 having an aperture 222 therein. The arm v2|4 on the shaft |02 which controls the yoke |10. is provided with a rearwardly extending arm 224 which terminates `iust short of the arm |44. An upwardly extending pin 226 is loosehr connected at its lower end with the free end of the arm 224 and loosely projects through the opening 222 in the arm-like' boss 220. A coil spring 226 loosely surrounds the pin 226 between .the arm 224 and thel arm-like boss 220. With this construction it will be apparent that when the pedal ill is moved to operate the brake through the servo mechanism the arm 224 will be rotated in a counter-clockwise direction of rotation and that upon application of the servo mechanism the arm |44 will also be rotated in a counter-clockwise direction of rotation. Thus upon application of the brakes the free endsof the arms 220 and 224 approach each other. v 226 are so proportioned and arranged that when the wheel brakes 24 are fully'taken up for wear and the brakes are fully applied by the servo mechanism the upper end of the spring 226 will approach but will preferably be in slightly spaced relation with respect to the under face of the arm 220. As the brakes 24 wear it will obviously require a greater movement of the arm |44 to fully apply them and, as the movement of the arm |44 to fully apply the brakes increases during wear of the brakes, a condition will be reached in which the lower face of the arm 220 will contact the upper end of the spring 226 during application of the brakes andconsequently compression of the spring 226 duringsuch application will occur. The operator of thevehicle in sensing the greater pressure required to apply the brak, because oi' the necessity of compressing the spring 226, will thus be acquainted with the fact that the brakes require adjustment 'for wear. Should this condition .be allowed to continue, a condition.

might eventually occur in which the spring 226 will be completely compressed and thus provide a` positive stop between the arms 220 and 2 24 preventing the vehicle operator from applying additional braking force to the yoke I00'and consequently the friction element 16. Thus with this construction means are provided whereby a .condition of excessive wear of the wheel brakes will prevent an over application of pressure to the servo-mechanism which would tend to foster its rapid or early destruction through wear of the friction lining ||6, for instance. and at the same 4thedriveshaftan'dthisconstructionwillbe desirable where the clearance between 'thelower face of the casing I4 and the ground i's'an important factor and must be maintained at amini- These arms and the length of the spring mumvalue. However, such construction necessitates the rod |50 being placed under compression during operation of the brakes and this is not always desirable. Accordingly, where the clearance between the casing 34 and the ground is of minor importance, the shaft |40 may be positioned below the shaft 46 as illustrated in Fig. l1, in which case the shaft |40 is indicated by an equivalent shaft |40'.` In such case the yoke |42 l0 is simply reversed in position, that is, its free ends project upwardly from the shaft |40 instead of downwardly as in the previousiigures. In such case the arm |44 is replaced by a double arm 230 fixed adjacent its center to the shaft |40' exteriorly of the casing 34. This permits arms 230 to be provided on either side of the casing 34 and thus permits the rods running to the rear wheel brakes, and which rods are here illustrated at |60', to be directly connected to the lower ends of the arms 230,*and permits the rods extending to the front wheel brakes, and which rods are here illustrated as at |62', to be directly connected to the respective upper ends of the arms 230, Consequently, in this construction all of the brake rods are in tension during operation of the brakes.

This last modification of the construction necessitates the modification of the construction illustrated in Fig. 10 to effect the same result. Accordingly, -a short arm 2.32 is extended rearwardly from the hub of the arm 230 and is pivotally connected by means of a pin 234 with an upwardly extending pin or rod' 236 which extends loosely through an aperture in the free end of an arm 238 fixed to and extending rearwardly from the arm 2|4 in the same general manner as the arm 224 previously described. In this case, however, the upper end of the rod 236 is provided with a stop member in the form of a nut 240v and between the nut 240 and the free end of the arm 230 40 a coil spring 242, corresponding to the spring 228 previously described, surrounds the rod 236. Preferably, a washer 244 rests against the upper end of the spring 242 for contact with the nut 240. This construction will operate in a ma er similar to that described in connection with g. 10, namely, upon application of the brakes the nut 240 and the free end of the arm 233 will approach each other and as the wheel brakes wear the washer 244 will eventually contact with the nut 240 and compression ofv the spring 242 will occur.

The constructions heretofore described are also applicable for use in connection with conventional types of hydraulic brakes and an application of the same is illustrated vin Figs. 12 and 13. In these figures a conventional master cylinder is indicated generally as at 250 and includes a casing 252 forming a liquid reservoir and provided with a cover 254. Within the lower part of the casing 252 is located the usual main cylinder 256 in which the usual piston 258 is adapted to reciprocate. It is to be understood, of course, that the liquid discharged from the cylinder 256 by the piston y 258 is conducted in a conventional manner to wheel brakes of the conventional hydraulic type. The casing 252 is secured to the cover 30 of the housing 34 by means of a suitable bracket 260 and screws 262. The shaft |40 is extended to within the casing 252 Where-anV operating arm 264 for the piston 258 is secured thereto. With this construction it be obvious that when the pedal 4|10 is depressed the servo mechanism will be operated to rotate the shaft |40 which, in moving the arm 264 in acounterclockwise direction of rotation, will actuate the piston 258 to force liquid from the cylinder 256 to the wheel brakes and cause actuation of the latter. With this construction in order to provide the same effect for preventing excessive application of the servo mechanism and to warn the operator of the necessity of adjusting the brakes for wear, an arm 220', corresponding to the arm 220 in Fig. 10, is secured to the shaft |40 between the casing 252 and the cover 38, and the arm 214 is provided with a second arm 224 as in Fig., 10 together with the rest of the parts described in connection with Fig. 10

for cooperation with the arm 220. VBy this mechanism the same result is effected as in the construction described in connection with Fig. 10.

The illustrations herein given are intended primarily as a matter of illustration only of the broader principles of the present invention and. once the teachings of the present invention are made known to thoseskilled in the art various modifications and changes in the specific illustrations given will be apparent to them and, ac-

cordingly, it will be understood that formal changes may be made in the specific embodiment of the invention described without departing from the spirit and substance of the broad invention, the scope of which is commensurate with the appended claims.

I claim:

l. In a servo mechanism, in combination, a driving shaft, a driving and a driven friction element, means moved by said driven friction element for applying an actuating force, means for effecting engagement of said friction elements, and means connecting said driving friction ele'- ment to said driving shaft so constructed and arranged as to exert a counter force in said second mentioned means proportional to the simultaneous value of said actuating force.

2. In a servo mechanism, in combination, a driving member, a driving friction element driven by said driving member, a driven friction element movably associated therewith, means moved by said driven friction element upon movement thereof by said driving friction element for effecting an actuating force, means for controlling engagement between said friction elements', and means associated with one of said friction ele. ments so constructed and arranged as to tend to separate said friction elements by a force proportional to the torque being transmitted through them.

3. In a servo mechanism, in combination, a driving member, a driving friction element driven by said driving member, a driven friction element .movably associated therewith, means moved by said driven. friction element upon movement thereof by said driving friction element for effecting an actuating force, means for forcing one of said friction elements into engagement with the other'thereof, and means associated with one of said friction elements so constructed and arranged as to oppose the force of said forcing means by a force proportional to the torque being transmitted through said friction elements. l

4. In a servo mechanism, in combination, a driving member, a driving friction element driven by said driving member, a driven friction element movably associated therewith,- means moved by said driven friction element upon movement thereof by said driving friction element for effecting van actuating force, means for forcing one of other thereof, and means associated with said one of said friction elements so constructed and arranged asto tend to separatesaid friction' elesaid friction elements into engagement with the ments against the force of said forcing means by a force proportional to the torque being transmitted through said friction elements.

5. In a vservo mechanism, in combination, a drivingmember, a driving friction element driven by saidAdriving member, a driven friction element.

driving friction element with said driving member so constructed and arranged as to oppose the force of said forcing means by a force proportional to the torque being transmitted through said frictionelements.

6. In a servo mechanism, in combination, a.

driving member, a driving friction element driven by said driving member, a driven friction element movably associated therewith, means moved by said driven friction element upon movement thereof' by said driving friction element for effecting an actuating force, means for forcing one of said friction elements into engagement with the other thereof, and cam means connecting said driving friction element with said driving member so constructed and arranged as to oppose the force of said forcing means by a force proportional to the torque being transmitted through said friction elements.

7. In a servo mechanism, in combination, a driving shaft, a friction element, means for shifting said friction element axially in one direction, a ,driving connection between said shaft and friction element so constructed and arranged as to tend to force said friction element in a direction opposite to the first mentioned direction upon the application of a force to said friction element tending to retard its rotation relative to said shaft, a second friction element rotatable relative to said shaft and engageable with the first mentioned friction element, actuating means movable by said second friction element upon rotational movement thereof.

8. In a servo mechanism, in combination, a driving shaft, a friction element, means for shifting said friction element axially in one direction,

.a driving connection between said shaft and friction element including cam `-means associated between said shaft and friction element so constructed and arranged as to exert an axial force in opposition to a force exerted by said shifting means proportional to a force resisting rotation of said friction element with said shaft, a second friction element rotatable relative to said shaft and engageable with the first mentioned friction element, and actuating means movable by said second friction element upon rotational movement thereof.

9. In a servo mechanism, in combination, a driving shaft, a friction element, cooperating cam elements on said shaft and said friction element tending to rotate one with the other and so con- 5 structed and arranged as to tend to move said friction element axially of said shaftby a force proportional to the torque being transmitted be tween it and said shaft, means for manually shifting said friction element in a direction opposite to that in which said cam elements tend lto shift it, a second friction element engageable by the rst mentioned friction element upon movement of the latter by said means, and 1 an actuating member movable by movement of said second friction element under the inuence of said first mentioned friction element.

10. In a servo mechanism, in combination, -a driving shaft, a friction element, a member fixed to said shaft for equal rotation therewith, a second member drivingly connected with the first mentioned member and bodily shiftable relative thereto diametrically of said shaft, diametrically opposite cam means on said second member and said friction element arranged in perpendicular relationship to the plane of movement of said second member relative to said first mentioned member and adapted to drivingly connect said friction element to said second member, a second friction element, means for moving the first mentioned friction element into driving engagement with said second friction element, and

an actuating member moved by movement of said second friction element under the influence of said first mentioned friction element.

11. In a servo mechanism, in combination, a driving member, a driven member, a driving and a driven friction element, means interconnecting in extent to the force simultaneously exerted by said driven member. v

`12. In a servo brake mechanism for wheeled vehicles, in combination, a driving element, a friction element rotatable therewith, a second rotatable friction\element adapted for engagement with the first mentioned friction element, cam means positioned on that side of said second friction lelement opposite to said first mentioned friction element and'rotatable with said second friction element, a second cam means slidably but non-rotatably mounted in cooperative relationship with respect to the first mentioned cam means so as to be moved axially thereby upon rotational movement thereof, wheel brakes actuated by axial movement of said second cam means, and means for moving said first men-A tioned friction element into engagement with said second friction element.

13. In a servo brake mechanism for vehicles having wheel brakes, in combination, a driving element, a friction element rotatable therewith, a second rotatable friction element adapted for engagement with the rst mentioned friction element, cam means positioned on that side of said second friction element opposite to said first mentioned frictionJ element and rotatable with said second friction element, means hunting movement of said second friction element toward said flrstmentioned friction element, a second cam means slidably but non-rotatably mounted in cooperative relationship with respect to the first mentioned cam means so as to be moved axially thereby upon rotational movement thereof, a rock shaft actuated by axial movement of said second cam means, ar connection beween said rock shaft and the wheel brakes for actuating the latter upon actuation of said `rock shaft, and means for moving said first mentioned friction element into engagement with said second friction element.

14. In a servo mechanism, ln combination, a driving element, a friction element rotatable 70 tion thereof, and means therewith, a second rotatable friction element adapted for engagement with the first mentioned friction element and supported independently of said shaft, cam means positioned on that side of said second friction element opposite to said first mentioned friction element and rotatable with said second friction element, means including an anti-friction bearing .limiting movement of saidsecond friction element toward said first mentioned friction element, a second cam means slidably but non-rotatably mounted in cooperative relationship with respect to the first mentioned cam means so as to be moved axially 'thereby upon rotational movement thereof, means actuated by axial movement of said second cam means; and means for moving said first mentioned friction element into engagement with said second friction element including a pedal and a connection between said pedal and said 20 first mentioned friction element setting up a reaction in opposition `to the force applied to said pedal proportional to the `torque transmittedv through said friction elements.

15. In a servo brake mechanism for automobiles having wheel brakes, in combination, a drive shaft, a friction element slidably mounted thereon and constantly rotatable therewith, a second friction element engageable with the first mentioned friction element, said second element be- `ing mounted for rotatable movement, a cam member rotatable with said second element and positioned on that side of said second element opposite to said first mentioned element, a second cam member held against rotation, antifriction means between said cam members, said cam members being so constructed and arranged and so cooperating with said anti-friction means that relative rotation between them effects axial displacement of one relative to the other, abutment means limiting axial movement of the first mentioned cam membervtoward said first mentioned friction element, an operating member arranged for operative movement upon axialy movement of said second cam member, a connection between said operating member and said brakes for effecting simultaneous movement thereof, and means for controlling the axial position of said first mentioned friction element.

' 16. In a servo brake mechanism forautomobiles having wheel brakes, `in combination, a driving element, a friction element rotatable therewith, a second rotatable friction element adapted for engagement with the rst mentioned friction element, a cam member on that side of said second' friction element opposite to said rst mentioned friction element and rotatable with said second friction element, a sec- 'ond cam member slidably but non-rotatably mounted in cooperative relationwith the first mentioned cam member, said cam members being provided with cooperating cams and rollers so constructed and arranged that said cam members are movable relative to one another through approximately at least 180 of rotation in effecting maximum axial displacement between them, means actuated Vby axial displacement between said cam members having an operative connection with said wheel brakes whereby to eiIect actuation of said wheel brakes upon actuafor moving said first mentioned friction element into engagement with said second friction element.,-

. 1'1. In a servo mechanism, in combination, a

pair of relatively shiftable friction members,

75.mans for rotatably driving one of said friction members, a pair of cooperating cam elements so constructed and arranged as to effect axial displacement between them upon relative rotation, rolling anti-friction members positioned between the cooperating faces of said cam elements, a ring member disposed outwardly of said cam elements in concentric relation thereto, means carried solely by said ring member for guiding said antifrictionkmembers, one of said friction members and one of said cam elements being arranged for simultaneous rotary movement, an operating member associated with and movable by the other of said cam elements, and means for controlling the engagement between said friction members.

18. In a servo mechanism, in combination, a pair of relatively shiftable friction members, means for rotatably driving one of said friction members, a pair of cooperating cam elements so` constructed and arranged as to effect axial displacement between them upon relative rotation, a ring member disposed outwardly of said cam elements in concentric relation thereto, a plurality of pins projecting radially inwardly from said ring, a roller rotatably mounted on each of said pins between the cooperating faces of said cam elements, one of said friction members and one of said cam elements being arranged Afor simultaneous rotaryv movement,' an operating member associated with and movable by the other of said cam elements, and means for controlling the engagement between said friction members.

19. In combination. a power shaft, a servo mechanism operable thereby, an actuating member movable by saidservo mechanism, a member movable to control the operation of said servo mechanism, and\means coacting between said control member and said actuating member for limiting the extent of actuation of said servo mechanism.

20. In combination, a power shaft, a servo mechanism operable thereby, an actuating member movable by said servo mechanism, a member movable to control the operation of said servo mechanism, and means movably associated with said control member and `said actuating member respectively and with each other for limiting the extent of actuation of said servo mechanism.

21. In combination, a power shaft, a servo mechanism operable thereby, an actuating member movable by said servo mechanism, a member movable mechanism, an element movable with said control member, and a, second element movable with said actuating member, said elements cooperating with one another to limit actuation of said servo mechanism.

22. In combination, a power shaft, a servo mechanism operable thereby, an actuating member movable by said servo mechanism, a member movable to control the operation of said servo mechanism, an element movable with said control member, and a second element movable with said actuating member, said elements having portions movable in opposition to each other during actuation of said servo mechanism and cooperating to limit the degree of actuation of said servo mechanism. p

23. In combination, a power shaft, a servo mechanism operable thereby, an actuating member movable by said servo mechanism, a member movable to control the operation of said servo mechanism, an element movable with said control to control the operation of said servo member, a second element movable with said actuating member, said elements having portions movable in opposition to each other during actuation of said servo mechanism, and resilient means cooperating between said oppositely movable portions to limit the extent of movement of one of said elements with respect to the other.

24. In a servo brake mechanism, in combination, a rotatable drive shaft. a member xed for rotation therewith, a second member frictionally engageable with the first mentioned member and adapted to be urged toward rotation therewith, cam means rotatable with said second member, braking means adapted to be actuated by said cam means, a pedal, means operable by said pedal for 'effecting frictional engagement of said members, and torque .responsive means in the line of connection between said cam means and said pedal so'constructed and arranged as to oppose vthe force applied to said pedal in proportion to the 'degree of torquesimultaneously transmitted between said members. i Y l 25. In a.A servo brake mechanism', inl-combination, a rotatable drive shaft, a member fixed for Y elements, braking meansactuated by movement of said driven friction element, and camfmeans 25PA rotation therewith', a second member frictionally engageable with the rst mentioned member and adapted to be urged toward rotation therewith, cam means rotatable with said second member, braking means adapted to be actuated by said cam means, a pedal, means operable byv said pedal for effecting frictional engagement oi' said members, and wedge means in the line of connection between said cam means and said pedal so constructed 4and arranged as to oppose the force applied to said pedal in proportion to the degree of torque simultaneously transmitted between said members.

26. In a servo brake mechanism, in combination, a rotatable drive shaft, a member fixed for rotation therewith, a second member frictionally engageable'with the flrst mentioned member and adapted tobe urged toward rotation therewith, cam means rotatable with said second member, braking means adapted to be'actuated by said cam means, a pedal, means operable by said pedal for effecting frictional engagement of said members, and cam and roller means .in the line of connection between said cam means and said pedal so constructed and arranged as to oppose the force applied to said pedal in proportion to the degree of torque simultaneously transmitted between said members. l

27. In a s'ervo mechanism, in combination, a rotatable driving shaft, a driving friction element rotatable therewith, a driven friction element engageable with said driving friction element and adapted., for rotatable movement thereby, pedal means for eiiectingV engagement;I of said friction in the connection'between said pedal and said braking means acting -to transmit the torque exerted between said driving shaft and driven friction element required to actuate said braking means, said cam means being so constructed and arranged as to resist actuation of said pedal means toward brake actuating positionin proportion to the amount of torque transmitted through it.`

ROBERT C. RUSSELL. 

